fx is a tiny, native coding agent CLI written in Zig that focuses on minimalism, performance, and embeddability.
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It acts as a shell-like coding harness that supports interactive sessions, automated tasks via subagents, and extensibility through MCP servers and custom skills.
- 01
Native binary with small footprint (~6 MiB) and high performance
- 02
Model-agnostic support for Vercel AI Gateway, Grok, Codex, and custom endpoints
- 03
Support for MCP servers and custom skill definitions for extended capabilities
- 04
Built-in permission system with auto-review modes for safety
- 05
Embeddable core (libfx) for Node.js and WebAssembly environments
Freemium
fx is open source, but model access requires subscriptions or API keys from providers like Vercel AI Gateway, OpenAI (Codex), or xAI (Grok). An optional 'Ultrafast' tier is available through AI Gateway at a higher price point.
Best for
Developers who need a high-performance, lightweight, and scriptable coding agent that integrates directly into terminal workflows and CI/CD pipelines.
Not ideal for
Users who prefer a full GUI-based IDE experience or those who cannot provide their own API keys or subscription credentials for model inference.
fx is a powerful, exceptionally fast coding agent for terminal power users who value minimalism and low-latency interaction, though it requires users to bring their own model subscriptions or gateway credentials.
Recent updates introduced the 'Ultrafast' inference tier for supported OpenAI models, active-turn steering via Ctrl+Enter, and major performance optimizations that significantly reduce launch, shell call, and session resume times. Additional improvements include simplified subagent interfaces, enhanced MCP management, and better context compaction.
As of
Is fx free?+
fx is Freemium. fx is open source, but model access requires subscriptions or API keys from providers like Vercel AI Gateway, OpenAI (Codex), or xAI (Grok). An optional 'Ultrafast' tier is available through AI Gateway at a higher price point. Check the official site for current plans.
Is fx open source?+
fx is not listed as open source on ai.dosa.dev - it is Freemium.
How much does fx cost?+
fx is open source, but model access requires subscriptions or API keys from providers like Vercel AI Gateway, OpenAI (Codex), or xAI (Grok). An optional 'Ultrafast' tier is available through AI Gateway at a higher price point. Pricing changes often - verify on the official site.
Who is fx best for?+
Developers who need a high-performance, lightweight, and scriptable coding agent that integrates directly into terminal workflows and CI/CD pipelines.
Who is fx not ideal for?+
Users who prefer a full GUI-based IDE experience or those who cannot provide their own API keys or subscription credentials for model inference.
What are the best fx alternatives?+
The closest fx alternatives on ai.dosa.dev are Claude Code, Codex CLI, Amp - all listed under Terminal & CLI Agents.
Who makes fx?+
fx is developed by Vercel. It is listed in the Terminal & CLI Agents category on ai.dosa.dev.
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